Transformer and reactor for fluorescent lighting units



0. KILTIE May 29, 1951 TRANSFORMER AND REACTOR FOR FLUORESCENT LIGHTINGUNITS Filed April 27, 1948 IN VEN TOR. Ora ear; hf/f/e Patented May 29,1951 UNITED STATES PATENT OFFICE TRANSFORMER AND REACTOR FOR FLUORESCENTLIGHTING UNITS Application April 27, 1948, Serial No. 23,514

2 Claims.

This invention relates to transformers and reactors of the type used inconjunction with fluorescent lighting tubes and is particularly directedto the core structure of such transformers.

Known reactors and transformers for fluorescent lighting units comprise,for the most part, cores made up of several difierent forms oflaminations held together by clamps or bars. The magnetic circuitsinvolved in these devices are necessarily such that the reactance of theunits is high and the fringing flux set up around the core is quiteextensive. Since the units are usually encased in metal there is a fluxlinkage between the core and the metallic case which sets up anundesirable vibration in the case so that the units hum, frequently tothe extent of annoyance to the user. Attempts have been made in the pastto prevent vibration of the cores by clamping the laminations tightlytogether either by bolts extending entirely through the cores or byclamping bands surrounding the stack of laminations. While suchexpedients may prevent noise which originates in the core itself theyhave relatively little effect on the noise produced by the case. If themagnetic path available to flux flowing in the outside legs of the coresis improved, the fringing flux and hence the noise resulting from casevibration, can be reduced.

The primary object of the present invention is to provide a transformerand ballast reactor for fluorescent lighting fixtures and similarinstallations which comprises a core made up of a single form oflamination and in which magnetic circuit is greatly improved.

Another object of the invention is to provide a core for a transformerand ballast reactor in which clamps and similar mechanical binding meansto hold the laminations against movement are eliminated.

Another object of the invention is to provide a core for a ballast andtransformer unit in which the impedance of the unit, and hence of theload, may be adjusted by increasing or decreasing the width of one ormore air gaps but in which such adjustment does not seriously affect themagnetic circuit in the remaining legs of the core.

Still another object of the invention is to provide a core for atransformer and ballast reactor which is capable of inexpensiie andrapid production and assembly and which will operate more eflicientlythan known devices over a wider range of frequency and with less noise.

Other objects and advantages of the invention will become apparent fromthe following speci- 2 fication, reference being had to the accompanyingdrawings in which Fig. l is a perspective View of an assembled core,several coils having been eliminated for purposes of clarity; Fig. 2 isa longitudinal sectional view of the core with the surrounding coils indicated diagrammatically; and Fig. 3 is a circuit diagram indicating theconnections between the unit and a pair of fluorescent lamps.

Referring to the drawings and particularly to Figs. 1 and 2, it will beseen that the core comprises sets of facing laminations made ofidentical stampings and results in a structure having opposed sides orbodies connected by legs I, 2, 3, 4, and 5. The laminations are soshaped that the outer ends which will comprise the legs I and 5 are ofdifferent length, one being shorter than the medial distance and theother longer than the medial. distance between the two opposed sides.The laminations which will comprise the legs 2 and 4 in the finalassembly are of the same length and are equal to slightly less than themedial distance from side to side of the finished core so that an airgap may be established in these legs.

The laminations which will comprise the center leg 3 are cut diagonallyfrom side to side so that a portion of the lamination extends beyond thecenter of the core and an equal portion is shorter than the medialdistance.

It will be seen that if the laminations so cut are brought face to facewith each other a butt joint occurs in the outside legs I and 5 and asimilar but slanting butt joint occurs in the center leg 3. However, bystacking a few laminations with the joints abutting, as indicated, andthen by stacking the next succeeding group of laminations oppositely,that is with the slope of the center laminations running in the oppositedirection as indicated in the dotted line in Fig. 2 and with the longerelement of that lamination which was previously indicated in the leg Inow reversed to occur in leg 5, an overlapping joint will be made in theoutside legs as at t and 8 in Fig. l and a similar overlapping joint asat Ii) will occur in the center leg. This reversal has no eiiect on thespacing of the laminations which comprise the legs 2 and t since aspreviously stated, these laminations are of the same dimensions.

It is preferred to repeat this reversal in ing up the core as shown inFig. 1 so that a small group, perhaps four or five of the laminations,meets its facing lamination in a butt joint and then the laminations arereversed so that an overlapping joint occurs betwee groups. The

magnetic path thus available for flux in the outside legs thus includesnot only the butt joint occurring between the small groups but also theoverlapping joint between successive groups. The

tions so that adjustments may be made in the air gaps in legs 2 and twithout seriously changing the reluctance of the path in legs I andSimilarly, adjustment of the air gaps in legs 2 and 4 does not seriouslyalter the magnetic characteristics of the center leg 3 since this,again, has. a magnetic path formed by overlapping joints betweensuccessive groups of laminations.

The windings are disposed on the legs in Such a manner that anauto-transformer winding is placed around the center leg 3 and a windingin which a component of the current is lagging with respect to thevoltage of the transformer is placed around the leg 2. The coil aroundthe leg 4 is preferably divided into two parts one of which is connectedin series with the trans former and with a capacitor to form a constantcurrent device in which there is a current component that leads thevoltage of the transformer. The other coil on the leg 6 is inductivelycoupled to the lead coil and may be used as a compensating coil in thecircuit.

In Fig. 3 the coil over the center leg is cated at T. The coil carryingthe lagging current is indicated at E2 and it will be seen that thiscoil is in series with one cathode of fluorescent lamp [3, the oppositeelement of said lamp being connected to the end of the transformer T.The coil carrying the leading current disposed around leg 4 is indicatedat I l in Fig. 3 and the capacitor with which it is in series isdesignated I5. This assembly supplies voltage to a lamp it, the cathodeof which is connected to the capacitor and to the compensating coilaround leg 4 which is designated l? in Fig. 3. Starting switches for thelamps are indicated at 8 and 49 respectively.

It will be seen that the flux linkages between the legs of the core aresuch that coils l2 and Hi can be utilized to add voltage to the voltagefrom the auto transformer T so that the size of the auto transformer maybe reduced in practice. It will also be seen that there are no loadedelements on the outside legs l and 5 so that the flux through these legsis unimpeded and does not contribute to the load current of the autotransformer T. Since the magnetic circuit in legs i and 5 is improvedover that which would be present with only butt joints between thelaminations the tendency for the flux to leave the laminations and enterthe surrounding case is materiallyfi'educed.

Assembly of the core is accomplished by stacking small groups oflaminations alternately and inserting them into the openings of theseveral coils and holding the coils in place with wooden wedges. Woodenor paper spacers may be used to determine accurately the size of the airgaps in legs 2 and 5. Prior to final assembly a coating of a plasticcement is applied to the overlapping portions of the small groups oflaminations. This cement will enter between the laminations themselvesbut more effectively will serve to hold the small groups tightly inplace since there is a substantial cemented area between the successivegroups of laminations in both the outside legs and in the center leg.

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It has been found that this cementing operation alone serves to hold thecore against vibration, and with the coils wedged in place around legs2, 3, and 4 the entire assembly is so free of noise that it may be useddirectly adjacent fluorescent lighting fixtures without objectionablehum. If desired, the entire reactor may be potted in the usualtransformer compound before placing it in the case.

It will be seen that, a single form of lamination being used for theentire unit, die cost is kept to a minimum and the assembly of the unitsis greatlyfacilitated over units in which a large number of diiierentlamination forms are required. It will also be seen that I have prO-vided a core which can be held together by cement alone Without thenecessity of using the usual clamping bands or bolts.

While the invention has been shown in connection with a specific formand disposition of the core legs it will be appreciated that niunerousmodifications and changes may be made therein without departing from thespirit of the invention as defined in the appended claims.

What I claim is:

1. A core for a transformer and reactor, which comprises a plurality oflayers of identical laminations stacked in facing relationship with twolaminations to each layer, a short leg and a long leg on opposite endsof each lamination, at least one other leg positioned between the endlegs which forms an air gap with its counter part on the laminationfacing it, said laminations being so stacked that overlapping joints areformed between certain successive laminations in each end leg and beingrelatively movable toward and away from each other to maintain saidfacing relationship and to increase or decrease the width of said airgap without breaking said overlapping joints, and a coil disposed aboutthe leg intermediate the end legs.

2. A core for a transformer and reactor, which comprises a plurality oflayers of identical laminations stacked in facing relationship with twolaminations to each layer, a short leg and a long leg on opposite endsof each lamination, a central leg midway between the end legs having oneside longer than the other so as to form an angled butt joint with itscounter part on the lamination facing it, a pair of legs located betweeneach end leg and the central leg, the laminations in said pair of legsbeing of such length as to provide air gaps therein, said laminationsbeing so stacked that overlapping joints are formed between certainsuccessive laminations in each end leg and in the central leg and beingrelatively movable toward and away from each other to maintain saidfacing relationship and to increase or decrease the width of said airgap without breaking said overlapping joints, and coils disposed aboutthe central leg and the adjacent pair of legs.

ORDEAN KILTIE.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 515,020 Ptiker -l Feb. 20, 18941,77'?,256 Daley et al. Sept. 30, 1930 1,869,364 Allison Aug. 2, 19322,397,646 Brown et al Apr. 2, 1946 2,460,145 Pfuntner et a1. Jan. 25,1949

